1. Field of the Invention
The present invention relates to a filter for removing water from water-containing oil and a method for such removal, and more particularly to a filter for removing water from water-containing oil which is composed of a fiber assembly formed at a particular density with a specific binder, and to a method for separating and removing water by passing the oil to be treated through said filter thereby transforming the water into coarse drops.
2. Description of the Prior Art
In recent years, there has been a strong demand for the realization of a technical means which makes it possible to lengthen the usable life of oil or to recover and reuse it by removing water, especially water which forms a stable emulsion, contained in organic liquids (oils) such as insulating oils, lubricating oils, organic solvents, etc. which are non-miscible with water. For this purpose, inorganic salts in the form of granules, for example, silica gel, zeolite, etc. are being used to some extent. Although it is possible to remove water to some degree by using these inorganic salts, their water-removing power is extremely low. In addition, such salts involve an intrinsic defect of remaining in the liquids in slight quantities after purification, and therefore their use has been limited. Also, the use of fibers having a certain degree of moisture- or water-absorbing properties, such as natural pulp, etc. has been attempted in some cases, but their water-removing ability has been very low, and poor from a practical standpoint.
We considered the instantaneous high water absorbing power and water holding power of water swellable polymers (hydrogels) and studied whether they could be utilized as a material for the removal of water contained in organic liquids. However, in the case of using a hydrogel in the form of granules, they swelled instantaneously and clogged the interspaces or gaps among the granules because of their excellent water-absorbing ability, and therefore we were obliged to stop the water removal treatment after a very short time. In order to avoid such gap-clogging, we tried to use a hydrogel in fiber form and found that it was possible to prolong the time of the water removal treatment to some degree in comparison with the case of granular hydrogels, but by reason of swelling and yielding of the fibers, we were not able to solve the problem of gap-clogging, and therefore it was impossible to cause such a fiber-form hydrogel to exhibit its water-absorbing power. Thereupon, as we proposed in Laid-Open Japanese Patent Application No. 106537/1980, we found that the use of a single element product from water-swellable fibers having a multi-phase structure composed of a hydrogel outer layer and an inner layer of an acrylonitrile polymer and/or another polymer or a compounded product of said fibers and other fibers, makes it possible to continue the water-removing treatment for a long time without gap clogging or yielding of the fibers, and to exhibit the water-absorbing power of the hydrogel.
By using the water-removing material described in this prior application, it has become possible to continue the water-removing treatment for a long time, but as apparent from its mechanism of action, it is impossible to continue the water-removing operation beyond the water-swellability (water-absorbing power) of the water-swellable fibers composing the water-removing filter. Accordingly, this filter is a means that can be used satisfactorily in the regeneration treatment of oil which contains trace quantities of water.